The official product page from Tamiya Japan is now up and gives us a a bit of new info.

Official release in Japan is March 22.

Translated text

42275 TRF503 Chassis Kit

★ belt drive 4WD buggy seeking the triumph of big race, TRF503 appeared.
★ stretched to 287mm wheelbase, I adopt the aluminum lower deck with improved gap drivability. Is set to 12 degrees front aluminum suspension plate, making it a cantilever type servo mount.
★ It is shipped with a big-bore-aeration damper of large capacity in suspension.

○ belt drive buggy fought IFMAR World Championship electric 4WD off-road class
– As a base, TRF latest series that incorporates the know-how obtained from the actual fighting
Buggy version of the machine.

○ become the new design almost non-Giyadefu suspension arms, and slim aluminum lower deck
– Balance of high-dimensional bending stiffness and by the combination of the upper decks. Phosphorus
The prime plenty of ambitious parts such as a new universal shaft of folly fixed
Was included. ※ body, battery, motor, RC mechanical, tire, wheel session
Are not supported.